https://www.hongkongairport.com/gb/passenger/departure/all/check-in-departure/passenger-departure-tax.html
http://www.cad.gov.hk/sc/for_travellers.html#tax
http://www.legislation.gov.hk/blis_pdf.nsf/6799165D2FEE3FA94825755E0033E532/F402F5C311FB572D482575EE00445FE1/$FILE/CAP_140_c_b5.pdf